The present invention relates to an electronic distributor ignition device for an internal combustion engine, especially an electronic distributor ignition device which controls changes of current limiting values.
In conventional electronic ignition devices, such as described in Laid-Open Japanese Patent No. 93471/1988, the maximum permissible primary current in the ignition coil is detected by reference to the voltage across the resistance of the hybrid IC conductor, which is divided in a voltage divider connected in parallel to the hybrid IC conductor, and is used to drive the current control transistor. In addition, a feedback circuit is used to extract current from the base of the power transistor.
One disadvantage of such prior art systems is that when the ambient temperature changes by as much as 100.degree. C., the current limiting value can also change by more than 30%, depending on the temperature characteristics of the emitter resistor and on the V.sub.BE of the current control transistor. It is therefore necessary to limit the current in order to protect the power switching element from damage caused by excessive current. If this current limiting value is set low, then the secondary voltage output from the ignition coil also drops, degrading the performance of the internal combustion engine. In addition, the amount of heat generated by the power transistor increases, as well. Thus, variation of the current limiting value should be kept small.
In the prior art, a feedback circuit is used, and as a result the power transistor is apt to oscillate, increasing the rate at which it generates heat, which is a problem. To eliminate this problem, a condenser must be inserted between the base of the power transistor and the base of the current limiting transistor.
An object of the present invention is to provide an electronic ignition device that can reduce substantially variations of the current limiting value caused by temperature changes.
Another purpose of the present invention is to provide an electronic distribution ignition device that can suppress oscillation of the power transistor.